http://www.ck12.org Chapter 28. The Physics of Global Warming Version 2
28.3 The Key Concepts (Physical Laws and Ob-
servations)
- The relationship between temperature of a body and its radiation wavelength is given byWien’s Law: For any
body that radiates energy, the wavelength of maximum energy radiated is inversely related to the temperature. - The effect of global warming on the solubility of Carbon Dioxide(CO 2 )and methane(CH 4 )is governed
by two laws that have opposing effects. Henry’s Law: The solubility of a gas is directly proportional to
the partial pressure of that gas. The constant of proportionality is Henry’s Law Constant. This constant of
proportionality is temperature dependent and decreases as temperature increases. Therefore as carbon dioxide
increases in the atmosphere the partial pressure ofCO 2 increases and more of it tends to dissolve in the oceans,
but as the temperature increases the constant decreases and less of it tends to dissolve. The net effect at a given
temperature will have to be calculated. - TheSolar Radiationpeaks at 610 nm; there is 61.2% of solar radiation is in the visible band( 400 −750 nm)
with less than 9% in the uv band and about 30 % in the near infra red. Some 99% is radiated between
275 and 5000 nm. This band largely is unabsorbed by any atmospheric gases. The most significant of the
greenhouse gases areH 2 OandCO 2. The plot above details the absorbance of various wavelengths of radiation
by atmospheric gases in the shortwave region. - TheEarth’s radiationpeaks at 11,000 nm, with an intensity of.04 W/cm^2. Some 99% is radiated between
40 ,000 nm and 3000 nm in the longer infrared regions. This band is unabsorbed by nitrogen, oxygen and
argon (99%) of the Earth’s current atmosphere), but partially absorbed by carbon dioxide, methane, water
vapor, nitrous oxide and some minor gases. The gases that absorb this band of radiation are calledgreenhouse
gases.
5.Earth Orbital Changes: There are three principal variations in orbit that are collectively known as the
Milankovitch Cycles. Atmospheric concentrations of methane closely followed this cycle historically and
on a larger time frame so have concentrations ofCO 2.
a. precession of the rotational axis (period: 23,000 years)
b. variation in tilt of rotational axis from 21. 5 ◦to 24. 5 ◦(period: 41,000 years)
c. eccentricity of the elliptical orbit (period: 100,000 years)
6.Departures from the historical cyclical trendbegan 8000 years ago with the development of agriculture.
This led to a temperature rise of 0. 8 ◦C above expected trends and concentrations ofCO 2 rising 30 ppm above
expected trends with the concentration of methane 450 ppb above natural trends. In the last 100 years of
industrialization these departures from normal have accelerated with temperature rising an additional 0. 8 ◦C
andCO 2 concentrations rising to 370 ppm, which is 90 ppm higher than the recordedCO 2 concentrations at the
warmest points in the interglacial periods. Methane concentrations are at 1750 ppb,1000 ppb above historical
highs. Over 70% of the extra greenhouse gases were added after 1950.CO 2 is emitted whenever anything
is burned, from wood to coal to gasoline. Methane is produced by animal husbandry, agriculture, and by
incomplete combustion or leakage of natural gas. As more greenhouse gases are put into the atmosphere
the temperature will increase further. The co-variation ofCO 2 concentrations and temperature has been
demonstrated not only by recent observation, but by records of the last 700,000 years from Antarctic ice
cores. There are many possible effects and feedback mechanisms that are currently being studied and modeled